server: fix learner metric incorrect issue

server/etcdserver/api/membership/cluster.go

@@ -284,6 +284,10 @@ func (c *RaftCluster) Recover(onSet func(*zap.Logger, *semver.Version)) {
 	onSet(c.lg, c.version)
 
 	for _, m := range c.members {
+		if c.localID == m.ID {
+			setIsLearnerMetric(m)
+		}
+
 		c.lg.Info(
 			"recovered/added member from store",
 			zap.String("cluster-id", c.cid.String()),
@@ -393,6 +397,11 @@ func (c *RaftCluster) AddMember(m *Member, shouldApplyV3 ShouldApplyV3) {
 	if c.v2store != nil {
 		mustSaveMemberToStore(c.lg, c.v2store, m)
 	}
+
+	if m.ID == c.localID {
+		setIsLearnerMetric(m)
+	}
+
 	if c.be != nil && shouldApplyV3 {
 		c.be.MustSaveMemberToBackend(m)
 
@@ -505,6 +514,10 @@ func (c *RaftCluster) PromoteMember(id types.ID, shouldApplyV3 ShouldApplyV3) {
 		mustUpdateMemberInStore(c.lg, c.v2store, &m)
 	}
 
+	if id == c.localID {
+		isLearner.Set(0)
+	}
+
 	if c.be != nil && shouldApplyV3 {
 		c.members[id].RaftAttributes.IsLearner = false
 		c.updateMembershipMetric(id, true)

server/etcdserver/api/membership/metrics.go

@@ -32,9 +32,24 @@ var (
 	},
 		[]string{"Local", "Remote"},
 	)
+	isLearner = prometheus.NewGauge(prometheus.GaugeOpts{
+		Namespace: "etcd",
+		Subsystem: "server",
+		Name:      "is_learner",
+		Help:      "Whether or not this member is a learner. 1 if is, 0 otherwise.",
+	})
 )
 
+func setIsLearnerMetric(m *Member) {
+	if m.IsLearner {
+		isLearner.Set(1)
+	} else {
+		isLearner.Set(0)
+	}
+}
+
 func init() {
 	prometheus.MustRegister(ClusterVersionMetrics)
 	prometheus.MustRegister(knownPeers)
+	prometheus.MustRegister(isLearner)
 }

server/etcdserver/metrics.go

@@ -44,12 +44,6 @@ var (
 		Name:      "leader_changes_seen_total",
 		Help:      "The number of leader changes seen.",
 	})
-	isLearner = prometheus.NewGauge(prometheus.GaugeOpts{
-		Namespace: "etcd",
-		Subsystem: "server",
-		Name:      "is_learner",
-		Help:      "Whether or not this member is a learner. 1 if is, 0 otherwise.",
-	})
 	learnerPromoteFailed = prometheus.NewCounterVec(prometheus.CounterOpts{
 		Namespace: "etcd",
 		Subsystem: "server",
@@ -171,7 +165,6 @@ func init() {
 	prometheus.MustRegister(currentVersion)
 	prometheus.MustRegister(currentGoVersion)
 	prometheus.MustRegister(serverID)
-	prometheus.MustRegister(isLearner)
 	prometheus.MustRegister(learnerPromoteSucceed)
 	prometheus.MustRegister(learnerPromoteFailed)
 	prometheus.MustRegister(fdUsed)

server/etcdserver/server.go

@@ -2060,15 +2060,6 @@ func (s *EtcdServer) applyConfChange(cc raftpb.ConfChange, confState *raftpb.Con
 			}
 		}
 
-		// update the isLearner metric when this server id is equal to the id in raft member confChange
-		if confChangeContext.Member.ID == s.MemberId() {
-			if cc.Type == raftpb.ConfChangeAddLearnerNode {
-				isLearner.Set(1)
-			} else {
-				isLearner.Set(0)
-			}
-		}
-
 	case raftpb.ConfChangeRemoveNode:
 		id := types.ID(cc.NodeID)
 		s.cluster.RemoveMember(id, shouldApplyV3)

tests/e2e/metrics_test.go

@@ -15,11 +15,14 @@
 package e2e
 
 import (
+	"context"
 	"fmt"
 	"testing"
+	"time"
 
 	"go.etcd.io/etcd/api/v3/version"
 	"go.etcd.io/etcd/pkg/v3/expect"
+	"go.etcd.io/etcd/tests/v3/framework/config"
 	"go.etcd.io/etcd/tests/v3/framework/e2e"
 )
 
@@ -37,6 +40,18 @@ func TestV3MetricsInsecure(t *testing.T) {
 	testCtl(t, metricsTest)
 }
 
+func TestV3LearnerMetricRecover(t *testing.T) {
+	cfg := e2e.NewConfigTLS()
+	cfg.ServerConfig.SnapshotCount = 10
+	testCtl(t, learnerMetricRecoverTest, withCfg(*cfg))
+}
+
+func TestV3LearnerMetricApplyFromSnapshotTest(t *testing.T) {
+	cfg := e2e.NewConfigTLS()
+	cfg.ServerConfig.SnapshotCount = 10
+	testCtl(t, learnerMetricApplyFromSnapshotTest, withCfg(*cfg))
+}
+
 func metricsTest(cx ctlCtx) {
 	if err := ctlV3Put(cx, "k", "v", ""); err != nil {
 		cx.t.Fatal(err)
@@ -69,3 +84,64 @@ func metricsTest(cx ctlCtx) {
 		}
 	}
 }
+
+func learnerMetricRecoverTest(cx ctlCtx) {
+	ctx, cancel := context.WithCancel(context.Background())
+	defer cancel()
+
+	if _, err := cx.epc.StartNewProc(ctx, nil, cx.t, true /* addAsLearner */); err != nil {
+		cx.t.Fatal(err)
+	}
+	expectLearnerMetrics(cx)
+
+	triggerSnapshot(ctx, cx)
+
+	// Restart cluster
+	if err := cx.epc.Restart(ctx); err != nil {
+		cx.t.Fatal(err)
+	}
+	expectLearnerMetrics(cx)
+}
+
+func learnerMetricApplyFromSnapshotTest(cx ctlCtx) {
+	ctx, cancel := context.WithCancel(context.Background())
+	defer cancel()
+
+	// Add learner but do not start it
+	_, learnerCfg, err := cx.epc.AddMember(ctx, nil, cx.t, true /* addAsLearner */)
+	if err != nil {
+		cx.t.Fatal(err)
+	}
+
+	triggerSnapshot(ctx, cx)
+
+	// Start the learner
+	if err = cx.epc.StartNewProcFromConfig(ctx, cx.t, learnerCfg); err != nil {
+		cx.t.Fatal(err)
+	}
+	expectLearnerMetrics(cx)
+}
+
+func triggerSnapshot(ctx context.Context, cx ctlCtx) {
+	etcdctl := cx.epc.Procs[0].Etcdctl()
+	for i := 0; i < int(cx.epc.Cfg.ServerConfig.SnapshotCount); i++ {
+		if err := etcdctl.Put(ctx, "k", "v", config.PutOptions{}); err != nil {
+			cx.t.Fatal(err)
+		}
+	}
+}
+
+func expectLearnerMetrics(cx ctlCtx) {
+	expectLearnerMetric(cx, 0, "etcd_server_is_learner 0")
+	expectLearnerMetric(cx, 1, "etcd_server_is_learner 1")
+}
+
+func expectLearnerMetric(cx ctlCtx, procIdx int, expectMetric string) {
+	ctx, cancel := context.WithTimeout(context.Background(), 5*time.Second)
+	defer cancel()
+
+	args := e2e.CURLPrefixArgsCluster(cx.epc.Cfg, cx.epc.Procs[procIdx], "GET", e2e.CURLReq{Endpoint: "/metrics"})
+	if err := e2e.SpawnWithExpectsContext(ctx, args, nil, expect.ExpectedResponse{Value: expectMetric}); err != nil {
+		cx.t.Fatal(err)
+	}
+}

tests/framework/e2e/cluster.go

@@ -780,7 +780,21 @@ func (epc *EtcdProcessCluster) CloseProc(ctx context.Context, finder func(EtcdPr
 // Phase 1 - Inform cluster of new configuration
 // Phase 2 - Start new member
 func (epc *EtcdProcessCluster) StartNewProc(ctx context.Context, cfg *EtcdProcessClusterConfig, tb testing.TB, addAsLearner bool, opts ...config.ClientOption) (memberID uint64, err error) {
-	var serverCfg *EtcdServerProcessConfig
+	memberID, serverCfg, err := epc.AddMember(ctx, cfg, tb, addAsLearner, opts...)
+	if err != nil {
+		return 0, err
+	}
+
+	// Then start process
+	if err = epc.StartNewProcFromConfig(ctx, tb, serverCfg); err != nil {
+		return 0, err
+	}
+
+	return memberID, nil
+}
+
+// AddMember adds a new member to the cluster without starting it.
+func (epc *EtcdProcessCluster) AddMember(ctx context.Context, cfg *EtcdProcessClusterConfig, tb testing.TB, addAsLearner bool, opts ...config.ClientOption) (memberID uint64, serverCfg *EtcdServerProcessConfig, err error) {
 	if cfg != nil {
 		serverCfg = cfg.EtcdServerProcessConfig(tb, epc.nextSeq)
 	} else {
@@ -808,20 +822,24 @@ func (epc *EtcdProcessCluster) StartNewProc(ctx context.Context, cfg *EtcdProces
 		resp, err = memberCtl.MemberAdd(ctx, serverCfg.Name, []string{serverCfg.PeerURL.String()})
 	}
 	if err != nil {
-		return 0, fmt.Errorf("failed to add new member: %w", err)
+		return 0, nil, fmt.Errorf("failed to add new member: %w", err)
 	}
 
-	// Then start process
+	return resp.Member.ID, serverCfg, nil
+}
+
+// StartNewProcFromConfig starts a new member process from the given config.
+func (epc *EtcdProcessCluster) StartNewProcFromConfig(ctx context.Context, tb testing.TB, serverCfg *EtcdServerProcessConfig) error {
 	tb.Log("start new member")
 	proc, err := NewEtcdProcess(tb, serverCfg)
 	if err != nil {
 		epc.Close()
-		return 0, fmt.Errorf("cannot configure: %v", err)
+		return fmt.Errorf("cannot configure: %v", err)
 	}
 
 	epc.Procs = append(epc.Procs, proc)
 
-	return resp.Member.ID, proc.Start(ctx)
+	return proc.Start(ctx)
 }
 
 // UpdateProcOptions updates the options for a specific process. If no opt is set, then the config is identical